1. Field of the Invention
This invention relates to a dilution material, a filter and an accessory for measuring infrared spectra.
2. Description of the Prior Art
When the infrared spectra of a material are measured, the sample is, in general, diluted prior to the measurement. Infrared spectroscopy is divided into the solution method, the paste method, the pellet method and the like according to the dilution method. Among them, the pellet method is widely utilized because of its superiorities with a small amount of a sample, sharp absorption spectra, no absorption spectra of a solvent, simple operation and the like. In the pellet method, the dilution materials for samples are potassium bromide, potassium chloride, sodium chloride, potassium iodide and the like, because they have no absorption peak in the infrared region and have plastic properties under pressure.
In the case of measuring the infrared spectra of highly scattering heterogeneous samples such as coals and pitches, infrared rays are scattered by the sample, and while a considerable quantity of infrared rays passes through the sample without contacting. Therefore, the background is great, and the absorption peaks are small. Heretofore, the background was eliminated by subtracting the baseline assumed to be straight lines or curves from the spectra (Y. Osawa, et al., J. Fuel Soc. Japan, 48,703, 1969, P. R. Solomon, et al., Fuel, 61,663, 1982). Such a correction method is inaccurate, because the supposed baseline composed of straight lines or curves is not the true baseline and is made by the perception of a human.